Safety control for fuel burners



Oct. 30, 1945. s. G. EsKlN ET Al. 2,388,130

SAFETY CONTROL FOR FUEL BURNERS Filed Jan. 20, 1944 T E' I H. ATTORNEY burner;

` l tion means.

`Patented oci. 3o, 194s s PATENT OFFICE SAFETY` CONTROL FOR FUEL BURNERS Samuel G. Eskin and Charlesl. Strobel, Pitts- Company, Youngwood,

Pennsylvania burgh, Pa., assignors to Robertshaw Thermostat v Pa., a corporation of Application January 20,1944. seria1No.51s,95s

1o claims.` (ci. 15s-111.1)

`This invention` relates to control systems and, moreparticularly, to combined safetyA and ignition i and. condition burners and the like.`

As disclosed in our copending application Serial No; 482,592, filed April 10, `194:3, a combined safety and condition controlling system may em t `ploy flame or heat sensitive devicesl for controlling operation `of` an'electromagnetic fuel `valve `which performs the dual function of safety and .condition control.; AWhere the flow of fuel to the main burner-is controlled `by electro- `magnetic means which is actuated in accordance with the condition of heat sensitive devices, it is importantin the interest of quiet operation to prevent the electromagnetic means from being (influenced by the variations in thermal conditions until these are stabilized and actuating values established. h l

fI'hisinVentiOn contemplates a complete sys` tem of the type indicated requiring no extranecus lgniting means for the burner and being relatively free from noise during the burner starting period. The invention thus has for an object the bringing` jof a safety and condition controlling system for fuel burners into operation bythe action of the burner igniting means. Another object ofthe invention isto insure quiet operation throughout the entire cycle and particularly during the starting period.

. Another object of the invention is to assure required timing of the sequence of operations which place the system inoperating condition.

Anotherobject of the invention is to cause the fuelfsupply to` be shutoff in the `event of leither powerfailure or the absence of a p Another` `object oftheziuvenuonis to mimmize the` effect of inrush current on the igni- Another object of the` invention is to render the "apparatus substantially uniform as to operatlng time over afi-ange` of operating condi- Other` objects andadvantages will become apparentfrom` the following description taken in connection with fthe` accompanying drawing,

, wherein y h Fig.1 is a schematic view of a combined safety,`

ignition and condition controlling apparatus for aI fuel burner embodying the invention;

Fig;` 2 is a schematic view of a detail in one operating position; andV ,y

. Fig. 3 is a schematic view of the same detail l in another operating position.

flame at the Vcontrolling means for fuel Referring more particularly to the drawing, a gaseous fuel burner l and an associated pilot burner I2 are shown as being supplied with fuel by a main fuel pipe i4.` The fuel supply vto both burners is controlled by a main valve I6 in the fuel pipe I4 and `which maybe manually operated. interposed in the fuel pipe Il between the main valve I6 and the burner Ill` is an electromagnetic or solenoidgas valve i8 of any known type which may be arranged, as in this instance, to be `opened when sufficient energizing current is supplied to the coil thereof and to be closed by gravity when such current is reduced below a certain minimum value. Operation of the main control valve I6 from closed to open position will permit flow of `fuel Vfrom the pipe i4 to the pilot burner i2, but fuel is not supplied to the main burner I0 unless the solenoid valve I8 is alsoin open position.

`Electric current for the operation of the apparatus is` supplied by the line wires 20cennected to theprimary of a transformer 22 which may receive commercial current at the primary at a voltage variation from |05 to |25 volts. In this embodiment, themain valve I8 has a main switch combined therewith which is connected t0 one'line wire 2|! by wires 2l and 26. Any suitable means may `be' incorporated in the combined valve and switch structure f6 to close the valve portion in accordance with the primary voltage variation above and vbelowan average of six volts.

Connected to one terminal of the transformer secondary by a wire`28 at a junction Als one branch of la parallelxmesh consisting of a flame sensitive elementfc and is connected at the other end by a wire 3| to the opposite junction B of the parallel'mesh. The elemental! is positioned adjacent the pilot burner l2 exposed to the heat of the flame thereof and will vary appreciably in resistance according to its heated or unheated condition.` The element 30 may be in the form of a coil of wire formed from material having normallya relatively low resistance and a positive temperature coeillcient of resistance, forming a ballast resistor. It will be apparent, however, that other types of name sensitive, heat responsive or thermal resistance elements hav` ing the required characteristics may be substituted and that it is not essential that the flame of the pilot burner actually impinge on the coil. Junction B is connected by a wire l2 with 'tact iii and the other end A limit-stop It is interposed mmol oi' the cut-out junction ci another parallel mesh included in the circuit, the'other junction D ofthis second parallel mesh. being connected by wire 3@ to the other terminal of the secondary of the transformer 22. @ne branch of this second parallel mesh consists of a resistance element 36 'which will be hereinafter designated as a valve control resistor. This resistor 3o is also preferably in the form of a coil of wire having normally a relatively low resistance and a positive temperature coeicient of resistance forming a ballast resistor, although as will be apparent hereinafter, a constant resistor could `be employed. The valve control resistor Sii 'is not, however, exposed to the heat oi any ame'but is adapted to. become heated upon passage of electric current therethrough and will changel its resistance appreciably in accordance with changes oftemperature caused by changes in the Value of current flowing through it.

other branch ci. the second parallel mesh `consists. of a constant resistance element 38, hereresistor forV the switch 39 coninaiter designated as a pick-upv solenoid valve it, and al control nected in 'series circuit cluding a bimetal arm il@ carrying on one end a pair of contacts -clisposed one on each side thereot and which'upon warping of the arm will engage alternately with contacts 42 and 46, designated hereinafter hot contact and cold contact, respectively, and spaced one from the other. The control switch 39 may be placed in the space to be heated by the main burner lil and the arm be subjected to the temperature variations therein forming a space thermostat or special form. It will be apparent that this space could well be an oven which is adapted to be heated by the main burner iii when in operation. The cold contact titi is preferably carried upon a second himetal arm fifi which is adapted to warp when heated. The arm. dit, however, 'is primarily responsive to the heating eect of a coil il adjacent thereto and having one end connected to conbetween the` bimetal arms it and it in position to be engaged by the Aarm till to restrain movement thereof toward the arm lli for a purpose which will be apparent hereinafter. The hot Contact @32 is connected by a wire ii@ with oneend ci a constant resistance element 52 hereinafter called the shuntlng resistor for solenoid Valve iii, the other end of this resistor 52 being connected by c wire alici mesh,` it will be apparent that another branch of this mesh includes a' cut-out kwhich is thermally sensitive and maybe of the slowacting, bimetallic snap-switch type.

connected by a wire and the other terminal thereof wire 551 to one terminal of the The other terminal of the solto iimcticn is connected by a solenoid valve iii.

enoid valve 'It is connected by a wire 56 to the Junction Bthus placing the ilamesensitive elementr till in parallel circuit with the cut-out 58 and solenoid valve iii.

In addition to the shunt established on the sclenod 'Valve iii by the flame sensitive element 39, this valve is also arranged to be short-circuited for o predetermined period of time. The temporary short-circuit. is established by a control relay in the `form ci mercury switches comprising timing elements t@ and 32 which are initially closed and embody predetermined time-delay petherewith. The control switch 3'@ may take the form of a thermostat J'npick-up resistor 38.

lOne ter-l a i l assenso 'onds while the timing element 62 has a delayed opening of approximately six seconds.` Variation in the delayed opening periods of timing elements '60 and 62 may be made as apparent hereinafter. It is to be noted, however, that both these timing elements are designed to close instantly although this arrangement is also subject to modification as will be explained hereinafter. Bothvl timing elements 60 and 62 may be operated as stated bythe common electromagnetic actuator 64 connected by Wire 66 to junction D and by wire 68 to wire 28.

The aforesaid short-circuity is established by the long delay timing element 60 on solenoid valve I8 and may be traced by a common wire 69 connected at one end to wire 53 and at the other end to a. wire 10 'anda Wire 1| connecting one adjacent terminal of each timing element 60 and 62 together while a wire 12 connects the other terminal of- 'the timing element 6I) with wire 3|. n

The short delay timing element 62 is adapted to control the energizatlon of an electrical igniting means 1S for the pilot burner I2, which igniting means may be in the form of a coil o1' wire adapted to reach incandescence upon passageof current therethrough. Thus, while Wire 69 'and wire 10 connect one` terminal of the timing element 62 to wire 53, the Vopposite terminal thereof is'con'- nected by wire 'I6 to one end of ignition coil 14, the opposite end of which is connected by'wire 18 to wire 34. Preferably, a constant resistance element 80 is included in the wire 18 to act as an adjusting resistor for the ignition coil 1 Y In order to bring the system ,into normal run- 40 ning operation themain valve I 6 is manually opened and will permit fuel to flow to the pilot iii to junction A of the first parallel mesh. Returning to the ilrst par-` burner III is as yet unheated and wire 16, ignition coil 14, g f ing resistor 80 back to the secondary of the transburner I2. Although such manual operation of themain valve I6 will serve to close the mainl switch incorporated therewith, the solenoid valve i8 is not energized at this time and no fuelcan iiow to the main switch two principal of valve I6 does, however,v energize circuits, one being the ignition circuit and the other theA solenoid Valve circuit. Moreover, the electromagnetic actuator 64' of the timing elements 60 and 52 is also energized kand will remain energized as long as the main switch of valve I5 is closed. It may be assumed thatthev oven/or other spaceto be heated by the main the control thermostat 39 has its cold vcontact 46 engaged with related contact on arm 40.

'Ifhe ignition coil circuit may be traced from' the transformersecondary 22 to junction A'wire 53,`wire 69, wire 10, short delay timing element 62 wire `18, including adjustformer v2.k The ignition coil 14 is thereforeen- Y ergized to igniting temperature and, afterl the pilot burner I2 is ignited thereby, the timing element 62 will be opened and the circuit become de energized. Thus, at the end of approximately six seconds, which is the time it takes for timing element 62 to undergo its delayed opening, the ignition coil is placed inv which is maintained for 'the `duration of the normal running period of the main burner II). As previouslymentioned, the six-second time-delay may be modified as desired 0f the delay period is retained.

main burner I0. The closing of the a deenergized condition 5 as long as the function 'v r The long delay timing element 88, which preferably does not open until after the expiration oi.'

an eighteen-second time-,delay period, maintains the `sl'iort-circuit on the` solenoid valve I8 during the initial ignition or starting period. The valve o l circuitatthis time consists of theseries arrange- A(nient o f the` transformer` secondary", the long delay timing` element 80 and the `second parallel lmesh of valve control resistor 35, pick-up resistor 3,8, lb imetalheater coil 4l and the cold contact 48 `engaged withthe related contact of bimetal arm 48. This circuit may be traced from the trans- `i'ormer secondary 22 to `junction A, wire 53, wire `83, wireilI, timing element 50, wire `12, wire 3|,

. i f wire 22 junction C ofthe second parallel mesh which` includes valve control resistor 36, bimetal arm, cold contact48, heater coil 41, pick-up resistor 38, junction D andfromthis Junction by wire.` to transformer secondary 22. l

The short circuit established by the long delay timing elementll on the solenoid valve I8 is reinovedwhen thistiming element opens the` circuit of wires 88, lland I2 at the expiration of the eighteen-second time-delay period. During this period theheat of the iiame of the pilot burner I2 i hascaused the ballast resistor 38 to become suflll i ciently heated and its resistance consequently to increased so that sufllcient current is supplied to the coil of` the solenoid valve I8 to cause actuaa' tion of this valve to open position. `It will be ob-` served that the pick-up resistor 88 for the solenoid valve I8 remains connected in parallel circuit with the valve control resistor 36 owing to the cold contact 48 of the controlthermostat 38 `being engazed with its related contact on arm 40. It will i j further be observed that although the resistance value oftheballast resistor 381s insuiiicient when this resistor is unheated by the pilot burner ilame in cause the solenoid valve I8 to be actuated to open position, such resistance `undergoes a gradu-` al increase in value as the ballast coil 38 becomes heated. Thus, it the short-circuit established by the timing element 88 on the solenoid valve I8 were dispensed with, the immediate actuation of valve )to open position `would not be assured and noisy` operation `during `the `gradual heatin of the ballast coil mightwell occur.

It `will now be apparent that th timing element 80 serves the joint purpose of insuring thatno fuel may ilow from the main burner Il'until after ignition of Vthe pilot burner I2 and, in the case of normal ignition, insuring immediate actuation of the solenoid valve I8 to open position at the end of the longer `time-delay period. However, as, long as the` short-circuit isremoved by operation of element 80 after the ballast resistor opening of thesolenoid valve I8 before `removal v of the short-circuit thereon, butpositive elimination of chattering` of thisvalve is accomplished by maintaining the `short-circuit for such period as will ensure the i ballast resistor reaching .such

temperature.

long .delay fOfperation oilthemain `burner Ill will serve to increase thetemperature ambientto the control thermostat 38 causing movement of the bimetal` arm 48 thereof toward the ho't contact 42. It may be assumed for the `purpose of this description i thatthe bimetal arm 48. now-movesto a neutral i position engaging neither the cold contact 48 nori the hotcontact 42. A circuit is then established `tromthe `transformer secondary 22, wire 34 to junction D,` valve control resistor 36; junction C, wire 32,` junction B, the parallel mesh oi solenoid valve I8 with its cut-out 58 andthe `ballast resistor 38, Junction A back to the transformer secondary 22. n In this `circuit the pick-up resistor 38 and the shunting resistor 52 are disconnected, as will be apparent, and the current through the coil of the solenoid `valve` I8 is, consequently reduced in value by removal of resistor 38 from parallel relation with the valve control resistor 38. However,` when the` bimetal arm 48 of control thermostat 39 moves as described from the cold contact 48 to neutral position the current value which flows through the coil oi the solenoid valve I8 is not reduced below the minimum value required to hold the valve in its open-or operating position, but the. circuit constants are adjusted at the lowest line voltage which may be i volts at the primaryso that the normal steady operat- Ai ter the mainburner Ill has been operating for some time the bimetal arm 48 may move to the hot contact position due. to the thermostat becoming satisedwhereupon a circuit arrangement is established from the transformer secondary `22A and the `valve control resistor 38 in series with the three-branch parallel mesh `,oiilame sensitive resistorSIl,v solenoid valve I8, and cut-out 58, and shunting resistor" 52. ,The resistor 52 is of such resistance value in shunt with the solenoid valve I8 as to cause this valve to return to closed position. i

Whenthe thermostat moves` from the hotcontact 42 back to the neutral position the solenoid valve I8 remains closed until the bimetal arm 40 warps suniciently toclose cold contact 48; `lin such event the cycle is repeated owing to the flame sensitive element 38 remaining heated by the ilameof the pilot burner I2. In case the flame sensitive element 38 becomes open-circuited suiiicient currentiiows through the cutout 58 to cause it to operateand cause .the-sclenoid valve I8 to close, providing the control thermostat iiilis` in either the coldcontact position or neutral position.` If however, the control thermostat 38 is in the hot contact position, the solenoid valve I8 is already closed due to the shunt-` tion, then thesolenoid valve I8 is already closed at the` time of llame failure. If, howevenwthe bimetal armltl` is `in the neutral position upon warping from the cold contact position, the solenoid valve vlil is open. The flame sensitive element 38 will cool in the absence ofthe pilot burner flame` and its resistance will decrease `causing a corresponding decrease in the current value to the solenoid `valve I8 which then closes. Suchv closing of the solenoid valve occurs in a relatively shorttime due to the combined action QI-the ballast resistor 38 and the valve control I resistor 3S. As previously described, the current which iiows through the coil of the solenoid valve Il in a neutral position of the thermostat is only slightly above the minimum value required to hold the valve in its open or operating position. Thus, by making the valve control resistor 36 sensitive to current changes, the decrease in voltage drop across the coil of the solenoid valve will be accelerated whenever an increase in resistance of the valve control resistor occurs upon cooling of llame sensitive resistor 30 and consequent increase of current through the valve control resistor 36. The resulting temperature increase in the valve control resistor 36 causes increase in voltage drop across the resistor and a rapid decrease in voltage drop across the coil of the solenoid valve I8.

In order to make the adjustment of the circuit constants less critical and the shut-off times of the solenoid valve comparatively short, the cold contact 46 of the thermostat is mounted on the bimetal arm 44. Thus, upon closure of the cold contact the himetal arm 44 will Warp from the position shown in Fig. 2 to that shown in Fig. 3. Even if the thermostat arm 40 remains in cold contact position, the contacts separate andre- J'oin several times as the arm 44 heats and cools upon automatic making and breaking of the circuit. Thus, the bimetal arm 44 serves' to open the cold contact 46 independently of the controlled temperature when the cold contact remains closed for a given length of time. The normal operation of the system is not aiected by this action of the arm 44 as once'the solenoid valve is actuated to open position it remains open until the hot contact is made. Due to the provision of the stop 48 the thermostat arm 40 is restrained from following movement of the arm 44 to the left as viewed in Fig. 3 and a separation of the cold contact 46 from arm 40 canoccur as soon as the arm 44 becomes heated by passage of current therethrough. Consequently, the separation of the cold contact has the same eiect as movement of the arm 40 to neutral position and the valve closing time is generally short.

It will vbe apparent that current could be conducted directly to the arm 44 in place of utilizing the heater coil 41 and such variation is within the scope of this invention. In case of power failure the solenoid valve is immediately closed and, as the actuator 64 of the mercury switch is deenergized the timing elements 60 and 62 are instantaneouslyreset for another time delayed opening. It will be apparent, however, that the long delay timing element 60 need not necessarily have an instantaneous closing action as long as it becomes closed before the short time-delay t' element 62 becomes open. That is, as the closing action of the long delay timing element .60 does not control the vclosing action of the solenoid valve I8 but only its opening, it is unnecessary that this timing element be closed at any time greatly in excess of the opening of the short delay timing element 62. However, as the `delayed opening of this timing element 62 is only six se'conds, it is apparent that instantaneous, or practically instantaneous, closing oi' the timing element 60 is desirable.

When the current supply is resumed after a failure thereof the transformer secondary 22 is again energized and the normal starting and running cycles of the system will be initiated. Should an open circuit occur in the ignition coil 14 then the system may be brought in operation by igniting the pilot burner I2 with a match and all of the safety features will be retained.

It will be understood that a, constant resistor could -be used in place of the current sensitive resistor 36 as the valve control. The systemwould then operate over a narrower range of voltages and the valve closing time would be increased.

` However, the system would not in such case be erated means connected to said quite as sensitive as the preferred form to rapid voltage variations and the advantages of reduced valve closing time and an extension of the primary voltage range over which the system will operate are believedsuperior. Considerable ilexibility of circuit arrangement results as the value of the respective resistances can be varied to suit diiierent operating conditions. The single solenoid valve functions as a condition and safety control in the arrangement described and a complete safety, ignition and condition controlling system has been provided. It will be apparent that various changes may be made in the-form and arrangement of parts and in the details of construction herein disclosedwithin the scope of the appended claims with ut departing from the spirit of the invention. 1

We claim:

l.4 A control system for Y fuel burners having main and pilot burners comprising in combination, a source of electrical energy, electrically operable means connected to said source for con` trolling the supply of fuel to the main burner, said means having an initial positionpreventing fuel supply to the main burner and being actuable to another position when current of sufficient value is supplied thereto, a resistance element in circuit with said controlling means and being adapted to vary in resistance in response to variations in current values in said circuit, a second resistance element shunting said controlling means and being located to be heated by the pilot burner, said second resistance elementl being adapted to vary in resistance in response to thermal variations therein caused by the heat of the pilot burner, and switching means having a timing element for short-circuiting said controlling means for a period during which said second resistance element is adapted to become heated, whereby suilicient current for causing actuation of said controlling means is supplied thereto following operation of said switching means to discontinue the said short-circuit.

2. A control system for fuelV burners having main and pilot burners comprising in combination, a source of electrical energy, electrically opsource for controlling the supply of fuel to the main burner, said means'having an initial position preventing fuelv supply tothe main burner and being actuable to another positionwhen current of sufficient value is supplied thereto, a resistance element in circuitl with said controlling means and being adapted to vary in resistance in response to variations in current values in said circuit, a. second resistance element shunting said controlling means and being located to beyheated by the pilot burner, said second resistance element being adapted .to vary in resistance in response to thermal variations therein caused by the heat of the pilot burner, means operable in conjunction with said resistance elements for decreasing the total resistance to current iiow in said circuit'while` said controlling means is in said initial position, and switching means having a timing element for short-circuiting said controlling means for e. period during which said second resistance elecientwcurrent for causing actuation `of said'controlling means is supplied thereto following `operi t ation or said switomog means to discontinue the g wohnort-circuit.

"control "system for fuel burners` having main dpilot burners comprising in combinational source of electrical energy, electrically op.`

erated` means connected to said source `for controlling the `supplyof fuel to the mainburner, means having an initial position preventing fuel supply to the mainV burner and beingactuable to another position when current of sunicient value `is supplied thereto, a resistance element in circuit with" said controlling means and being 'adaptedto vary in resistance in response to variations in` current values in said circuit,.a second resistance element t shunting i said controlling ment in series circuitwith said controlling means and being capable of increasing substantially' `in its` resistance upon passage of current therethrough. and a second resistance element shunt@b means and being locatedto be heated by the pilot Y burner-,1 said second resistance element being ,adapd to vary in resistance in response `to ther- .mal variations therein causediby the heat of the pilot burner, a third resistance element shunting theiirstf said resistance and thereby decreasing the total resistance to currentiiow in said circuit whilesaidfcontrolling meansisin said initial position, switching means having atiming element for short-crcuiting said controlling means element isadaptedftoibecome heated, whereby continuing the shunt established by solo third resistance element and thereby causing only sumcient ein-rent toghe supplied tosaid controlling `m ns tomaintiin it in said other position.

d." A" comb ignitionand control system for fuel burners having `main and pilot burners, comv y y assenso 5 t mentisadapted to become heated, whereby suni` for a predetermined period, igniting means for the pilot burner having separate connection with `said source, second switching'means having a timing element for electrically. disconnecting said igniting means after a predetermined pexiodless than that ofthe first said timing element, electromagneticmeans common to both said switch ing means for operating the same simultaneously to initiate said timing periods, a resistance ele-v ing said controlling means andbeing capable of increasing substantiallyin its resistance as its temperature increases, said second resistance element being exposed to the heat of the pilot burner and causing sufllcient current to"be supplied to said controlling means for operation thereof from said initial position following exupiration of Vthe period of the first said timing ele-` ment.

8. A controlsystem for fuel burners having main and pilot burners comprising in combination, a source of electrical energy, electrically operabie means connected tosaid source for confor. a period during which saidsecond resistance '30 controlling means is supplied thereto following trolling the` supply of fuel to themain burner, said means having an initial positionpreventing fuel supply to the main burner and being actuable to another `position when current of sufiicient value is` supplied thereto, a resistance element in circuit with said controlling means and being ,f adapted to vary in resistance in response to variaprising` a source of electrical energy. electrically means connected to solo source for ooni tr011km fuel Asimply to thsmsin burner und hsving an initial position in which said fuelsupply for apred'etermined period, igniting means for the pilotburner having a separate connection withsaid sourceysecond switching means having a timing element operable for electrically disconnecting said ignlting means after a predetermined period independent of that of the first said timvalues inthe said circuit thereof, and a second resistance i element shunting said controlling means and being capable of increasing substanis? prevented, switohingmesns having s` timing element short-ch'cuiting o said controlling means i, and causing it to remainin said initial position i tions in current `values in said'circuit, a second resistance element shunting said controlling means and' being llocated to be heated bythe pilot burner, said second resistance element being adapted to vary in resistance in response to thermal variations therein caused by the heat of the pilot burne switching meanshaving' a tim- .ing' element for short-cirouiting said controlling;

means `while said second resistance `is becoming heated,` a thermally operable switch responsive to conditions caused by operation of the main burner, and meanscontrolledby said thermally operableswitch for shunting the nrst said resistance element in the initial position of said controllingmeans. Y C e t "LA control system for fuel burners having main and pilot burners comprising in combination, a source of electrical energy, electrically operable means connected to said source for controlling the supply of fuel to the main burner.

tially in its resistance as its `temperature increases, Y

, said second resistance element being exposed to the heat of the pilot burner and causing sufiicient current to be supplied to said controlling means ffor operation thereof from said initial position following expiration of the period of the first said timing element.

"' a combined ignition suuooutroi system for fue! burners having main and pilot burners,` comprising a source of electrical energy, electrically operable means connected to said source for con-- trolling fuel supply to the main burner and havtion in'which said fuel supply ine summon iapseve'nted.switchingmeanshavingatiming said means having an initial position preventing fuel supply to the main burner and being actuabie to another position when current of suiiicient value is supplied thereto, a resistance element in` circuit with said controlling means and being adapted to vary' in resistance in response to variations in current values in said circuit, a second` resistance element shunting said controlling' meansand being located to be heated by the pilot burner. said second resistance element' being adaptedto vary in'resistanceinresp'onscto thermal variations therein caused by the heat of the pilot burner, switchingmeans havingV a timing element for short-circuiting said controlling meansl while said second resistance is' becoming heated, a third resistance element, and a there maliy operable switch responsive to conditions caused by operation of the main burner and cooperable withsaid third resistance forl shunting the first said resistance in the initial position of said controlling means, said being lactuable is permitted. switching means lhaving a vtimingseries -circuit with said controlling means and being capable of increasing substantially in its resistance upon passage of current therethrough, a second'resistance element shunting said controlling means and being capable of increasing substantially in its resistance as its temperature increases, said second resistance being exposed to the heat of the pilot burner, switching means having a timing element for short-circuiting said controlling means while said second resistance is becomingl heated, a third resistance element having fixed impedance value, anda thermally oper'abie switch responsive to conditions caused by operation of the main burner and cooperable with saidthird resistance for shunting the iii-st said resistance in the initial position of said controlling means; said thermal switchv being operable in said other position of said controlling means for discontinuing said first resistance shuntduring'f'operation o! the main burner.

9. A combined ignition and control system for fuel :burners having main and pilot burners. 'comprising a source of electrical energy,` electrically operable means connected `to said source for controlling fuel supply to the mainv burner, said controlling means having an initial position lin which said fuel supply is prevented and being to another position where fuel supply element short-eircuiting said controlling means and causing it to remain in said initial position for the pilot burner having separatev connection with said source, second switching means having a timing element forelectrically disconnecting said igniting means after a predetermined period independent of that `oi' the nrst said timing element. a resistance element in controlling means and being adapted to vary in response to variations in current resistance in a predetermined`period,`igniting means for circuit with said values in the said circuit thereof, a second resistance element shunting said controlling means and being located to be heated by the pilot burner, said second resistance element-being 5 adapted to vary in resistance in response te there mal variations therein `caused by the heat of the pilot burner, and a thermally operable switch responsive to conditions caused by operational l the mainl burner and being operable for shuntl itial positionv of said controllingmeans.

i 10. A combined ignition and controlV system for fuel burners having main and pilot burners, comprising asource of electrical energy,y electrically operablefmeans connected to said source for controlling the fuel supply to the main burner, said controlling means having an initial position where said fuel supply is prevented yand being actuable to another position in which fuel supply is permitted, switching means having a timing element short-clrcuiting said controlling means and causing it to remain in said initial position for a predetermined period.A means for vthe pilot burner having separate con-` nection with said source, second switching means having a timing element for electrically disconnecting said igniting-means after a predetertially in lts resistance `vupon'passagfe of current f second resistance element shunting said controlling means and being capable of increasing vsubstantially in its resistance as its temperature increases, said second resistance ele-i 40 ment being exposed to the heat of the pilot burner, a third resistance element, and ka, ther-` the first saidresistance in the initial position of said controlling means, said thermal switch being operable in said other position of said controlling means lfor discontinuing said first resistance o shunt during operation of the main burner. Y

SAMUEL d. y CHARLES' K ls'rnoaar..

ing the first said resistance element in the; in-

mating lessthan that cf the first said tixn-` f 

